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  1. #1
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    Default Making cast whitemetal (babbitt) bearings.

    I’ve just finished making the main bearings for my model engine and thought others might find some of this interesting.
    There will be a lot of photos in this thread.

    The main bearings of this engine are of the cast white metal variety so the bearing housings were bored out to 1.125” which allows for the bearing to be bored to 7/8” leaving 1/8” of babbitt material all round for the bearing itself.

    The bearing caps were secured onto the crankcase casting and the centre location of the main bearings marked out. The crankcase was mounted on the mill table then aligned and centred with the horizontal spindle ready for boring operation. A slot drill was used to produce a small flat which would prevent a drill from wandering when starting. The pilot hole was spotted with a centre drill then a 6mm stub drill was used to go right through. The pilot hole was then opened up using a 1/2” stub drill then a 5/8” MT2 drill bit.

    Main Bearings 01.jpg
    Ready to drill the first pilot hole through the casting with a 6mm stub drill.
    Main Bearings 02.jpg
    The pilot hole was increased first using a 1/2” stub drill then with a 5/8” MT2 drill.

    With the first bearing pilot hole opened up to 5/8” the pilot hole for the second bearing was drilled. A 100mm ER11 chuck was mounted in the spindle to reach through the casting and hold the slot drill, centre drill and 6mm stub drill before going straight through with the 5/8” MT2 drill to finish the pilot hole.

    Main Bearings 03.jpg
    Centre drill mounted in an ER11 chuck to spot the pilot hole.
    Main Bearings 04.jpg
    The 5/8” MT2 drill ready to finish the second pilot hole.

    It was at this point I discovered two flaws in my setup of mounting the crankcase flat on the mill table and using the horizontal spindle for the boring.

    The first was that the casting had moved slightly under the load of drilling the second pilot hole meaning it was no longer correctly aligned with the first bearing or the cylinder mounting face. This was not a huge problem as there was still plenty of material left and this could be easily rectified during the final boring operation. I should have mounted a positive stop behind the casting to prevent this from happening, but the thought did not occur to me at the time.

    The second problem was a bit of a show stopper for this setup though as there was not quite enough room to mount the boring head in the horizontal spindle and still have clearance for the extended boring bar to machine the first bearing. I could have used a shorter bar for the first bearing then used the longer bar for the second one, but the long bar is solid carbide so it’s very rigid and I preferred to do both bearings in the same pass.

    It’s at times like this that I really love my Thiel mill because I can remove the universal table and mount work directly to the X axis slide. After a bit of juggling, the crankcase was mounted to the X axis vertical surface and aligned to the vertical spindle making sure to include a positive stop under the case this time. I also left the parallel used to align the casting in the correct plane in place and used a DTI to monitor if any movement occurred during the boring operation.

    Main Bearings 05.jpg
    Crankcase casting mounted directly to the vertical X axis slide.
    Main Bearings 06.jpg
    Another view of the crankcase mounted on the mill showing the positive stops, the parallel and DTI.
    Main Bearings 07.jpg
    Action shot of the boring operation, this is about three quarters through the second bearing housing.

  2. #2
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    Default

    The main bearing housings needed some anchor points to prevent the babbitt from moving. Using a 6mm end mill two keys were milled on either side of the crankcase and one on either side of the bearing caps. The 100mm ER11 chuck came in handy again for this operation.

    Main Bearings 08.jpg
    Cutting the babbit anchors into the crankcase.
    Main Bearings 09.jpg
    The finished babbit anchors.
    Main Bearings 10.jpg
    View of the anchor positions with the bearing assembled.

    The inner sides of the crankcase were also faced to 1.675” to remove the pattern draft, mainly so the components of the bearing mould & core would sit flat and parallel against the crankcase.

    Main Bearings 11.jpg
    View of the setup for facing the inner side of the bearing housings.

  3. #3
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    With the bearing housings bored and keyed everything was now ready to pour the actual bearings but finding a source of babbitt was not as easy as I at first thought it would be. I visited a couple of different bearing shops with no luck and it was only when contacted BRS Bearing Remetalling Services in Doveton (Victoria, Australia) that I managed to find some. They agreed to sell me a kilo for $50.00 but when I called in to pick it up they gave me a chunk weighing closer to two kilo which should be enough to last me a long time.

    Due to the size of the bearings I didn’t want to pour the two halves as solid plugs of Babbitt. I made up a mould / core fixture that would allow the bearings to be poured with a 0.625” void to keep the wall thickness to 0.250” which I hoped would prevent any shrinkage problems.

    One end of the fixture is an interchangeable threaded bush which is clamped in the bearing not being poured to centre the core assembly. The 0.625” core has two flat wings that separate the two halves of the bearing and a disk which forms the base of the mould. The two semicircular pieces are clamped onto the protruding wings to form a riser dam which feeds the mould as the babbitt cools to reduce shrinkage.

    Main Bearings 12.jpg
    The bearing mould / core fixture.

    The areas of the core / mould fixture that will be in contact with the babbitt were blackened over some burning kero to act as a release agent preventing the babbitt from adhering. A 1.125” bush was fitted on the fixture and it was installed on the crankcase and clamped in place with a piece of aluminium shim under the bearing cap. The cap of the bearing to be poured was clamped down over the wings of the fixture and the disk tightened up against the inside edge to seal the bottom of the mould before the riser pieces were clamped into place. The last step was to plug the oil hole in the bearing cap to prevent the babbitt from escaping through it, for this I used an aluminium pop rivet which just so happened to be the right size. The crankcase was then positioned on its side and chocked from beneath to sit level and it was ready to pour the bearing.

    Main Bearings 13.jpg
    The bearing mould / core fixture before fitting the bearing caps.
    Main Bearings 14.jpg
    And clamped by the bearing cap for the first bearing.
    Main Bearings 15.jpg
    Everything in place (except the rivet) ready to pour the first bearing.

  4. #4
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    I’m using a tin based babbitt with a pouring temperature of around 430⁰C. While the low melting point makes working with babbitt fairly easy it is important to be careful with the temperature. Obviously, if the metal is too cold it may start to set half way through the pour resulting in an unusable bearing. However, if it is allowed to get too hot or left in the molten state for too long, the metallurgical properties can change as lower melting point metals burn off. A laser thermometer is probably the best way to monitor the temperature but I don’t have one so I relied on a more primitive method. A small piece of pine (I used an icy-pole stick) immersed in the molten babbitt for a few seconds will just start to blacken if the temperature is correct. If the stick doesn’t blacken it’s not hot enough, if it ignites it’s too hot. Not as accurate as a thermometer but by all accounts a valid method and it worked ok for me.

    Preheating the bearing housing before pouring is an important step as pouring the molten babbitt into a cold shell will result in any number of failures due to the babbitt cooling too quickly. The metal may start to set before the pour is finished resulting in a short pour or an uneven bearing substrate. The bearing may shrink away from the housing and not be retained properly allowing movement. I used an LPG torch with a fairly large burner to preheat the crank case before pouring each bearing. The crankcase was heated until the area around the bearing was hot enough to sizzle when touched with a wet finger. Ideally it should probably have been a bit hotter but given the size of the casting this was about the best I could practically do given the torch I was using.

    Main Bearings 16.jpg
    Preheating the crankcase (this was actually before pouring the second bearing).

    My melting pot, made from a piece of 1.5” steel pipe with some 12mm threaded rod for a handle, was pre charged with a few of chunks of babbitt cut from the larger ingot and the same LPG torch was used for the melt.

    Main Bearings 17.jpg
    Melting the babbitt.
    Main Bearings 18.jpg
    How the test stick should look when temperature is within range.

    The LPG torch was swapped back and forth a few times between the crankcase and the pot to make sure everything was at the right temperature and the babbitt was given a gentle stir to ensure even consistency before completing the pour. Each half of the bearing is done as a single continuous pour. I poured the crankcase half first, immediately followed by the bearing cap half. The trick is not to let the first pour overflow into the second half and with hindsight I should have made the wings on the core a bit longer to match the height of the riser ring but in the end it all worked out ok.

    Main Bearings 19.jpg
    Action shot of the first bearing pour.
    Main Bearings 20.jpg
    View of the completed pour after it had set.

    After the pour everything was left to sit while the bearing cooled. In theory I should probably have pre tinned the bearing housing to guarantee the shells adhere to the walls but I thought I would just do the pour and see how things went. After around twenty minutes I disassembled everything to inspect the pour and was pretty happy with the result. The babbitt had flowed nicely, filled the anchor keys and not pulled away from the sides of the housing. There was no discernible movement of the shells within the bearing cap or the crank case housings so all was good.

    Main Bearings 21.jpg
    The freshly poured bearing cap.
    Main Bearings 22.jpg
    The crankcase babbitt shells.

    With the first shell a success it was a on to the second one. The same setup was used with a 0.625” bush on the mould / core fixture allowing it to be clamped in the first bearing. Everything else was a repetition of the first pour and the result was pretty much the same.


    Main Bearings 23.jpg
    The second completed pour.
    Main Bearings 24.jpg
    View of the two crankcase bearing shells.

  5. #5
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    With the babbitt pours successfully done the next job was to trim the risers off. The plan was to use a slitting saw but I wanted to be sure the bearing shells wouldn’t move during the process so an improvised clamp was made up to ensure the shells stayed in place during the cut.

    Main Bearings 25.JPG
    View of the strap clamp in use.
    Main Bearings 26.jpg
    Action shot trimming the risers.
    Main Bearings 27.jpg
    View of the bearing with the riser trimmed back.
    Main Bearings 28.jpg
    And from above.

    Before the bearings could be bored to size I needed to make some shims to go between the crankcase and bearings caps to allow for adjustment to compensate for wear over time. I used two 0.0015” shims, one 0.002”, one 0.003” and one 0.004” shim on each bearing cap stud. Cutting the shims to the correct size was easy enough, I just used a sharp set of tin snips. To put in the holes, a small jig was made to clamp a stack of five shims in a tight pile between a guide hole that allowed the shims to be drilled using an 8mm slot drill.


    Main Bearings 29.jpg
    A few shims along with the jig for drilling the holes, the shim thickness was marked with permanent marker.
    Main Bearings 30.JPG
    The shims stacked on each stud.
    Main Bearings 31.JPG
    View of the bearing cap installed with the shims in place.

  6. #6
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    With the caps shimmed the bearings were now ready to be bored to size using pretty much the same setup as that used to bore the bearing housings. The use of a sharp, high positive rake HSS tool is usually recommended to machine babbitt but I wanted to stick with the solid carbide boring bar so I used a polished high positive rake aluminium insert. Running at 210 RPM this produced a nice finish in the babbitt which machines very easily as you might expect.

    Main Bearings 32.jpg
    Mill setup for boring bearing shells.

    To get the bearings to the required 0.875” required the removal of around 0.125” of material. A couple of initial cuts were made to get the bearings circular in shape before a reference measurement was taken to calculate exactly how much more material needed to be removed. A couple of heavier cuts were made to bring the bearings to 0.833” ready for a couple of finishing cuts to get to the final size.

    The facing stop on the UPA-4 can be used in conjunction with gauge blocks to make very accurate adjustments, this is particularly useful when working to an imperial size with a metric boring head.

    Fist measure the bore and calculate the depth of cut needed to bring the bore to the final required size, in this case (0.875-0.833)/2 = 0.021”. I wanted to make two cuts to reach the final size, one of 0.018” and a finishing cut of 0.003”.

    Assemble a stack of gauge blocks to a total ending in the amount required for the cut. In this case I made a stack from the following blocks: 0.100 + 0.110 + 0.080 + 0.100, giving a total of 0.418”, the two 0.100 being wear blocks.

    Place the stack between the stop plate and pin of the UPA-4 and clamp the stop plate to reference the position of the boring head.

    Main Bearings 33.JPG
    Initial gauge block stack in place between the stop plate and pin of the UPA-4 boring head.

    Assemble a second stack of gauge blocks smaller than the initial stack by the amount the head needs to be adjusted, in this case 0.400” (0.100 + 0.200 + 0.100), then adjust the boring head until this stack is a sliding fit between the stop plate and pin. The boring head will now take a cut of exactly the difference between the two gauge block stacks, which in this case was 0.018”.

    Main Bearings 34.JPG
    Boring head adjusted to size of second gauge block stack.

    Using this method removes the possibility of errors caused by misreading the adjustment scale or from backlash in the boring head adjusting screw. The procedure was then repeated to set the boring head to make the final 0.003” cut and the bearings were bored to exactly 0.875”.

    Main Bearings 35.JPG
    A view of the 0.018” cut showing the surface finish.

    The outer flange of each bearing was faced off using the UPA-4 and a 45⁰ chamfer cut on the outer bearing edge. The bearing caps were then removed and the oiler holes drilled through the bearing and slightly countersunk.

    Main Bearings 36.JPG
    Setup for facing off the outer flange of the bearing shells.
    Main Bearings 37.jpg
    A view of the bearing cap bored to final size and ready for fitting with the crankshaft.

  7. #7
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    With the main bearings bored to size it was time to fit the crank shaft and finally see something come together. A couple of spots of bluing compound were applied to the crank shaft before assembly to give an indication of any high spots that required scraping. With the bearings assembled, the crank was able to be rotated with some slight binding. Some binding on the initial fit is a good thing because this means only a little scraping is required to bring the bearing to the required fit. If the shaft had been a loose fit then some shims would have to be removed and more substantial scraping performed to fit everything correctly.

    Main Bearings 38.JPG
    The crank shaft fitted for bluing.

    The bearings were disassembled and the points that were binding were clearly indicated by the locations where the blue had transferred to the bearing shells.

    Main Bearings 39.JPG
    The bearings disassembled after a bluing cycle.
    Main Bearings 40.JPG
    The blue areas indicate the high spots.

    The high spots were scraped back using a three lobe bearing scraper and everything reassembled and the process repeated until the crank rotated freely and the blue transferred evenly across the bearing surface.

    Main Bearings 41.jpg

    Main Bearings 42.jpg
    The three lobe scraper used to scrape the bearings.
    Main Bearings 43.jpg
    The bluing pattern after the bearings have been scraped to fit.
    Main Bearings 44.JPG
    And the crankcase.

  8. #8
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    The last step was to add some grooves to distribute oil evenly around the crank shaft. I went with cross pattern oil groves which were first marked in using a texta before a Dremel fitted with a 3mm carbide ball burr was used to cut them in. The groves were cut freehand and I was aiming for a depth of around 1/32”. Being soft, the babbitt cut very easily so I had the Dremel rotating at the second slowest speed and had to be careful to keep the tool moving to prevent it from digging in. As can be seen, a couple of the grooves came out a bit wonky but they should do the job. Last step was to chamfer the edges of the grooves using a scraper ground from a hacksaw blade.

    Main Bearings 45.JPG Main Bearings 46.jpg
    View of the oil grooves cut into each bearing shell.

    A couple of drops of oil were placed in the bottom of the crankcase shells before fitting the crankshaft. A couple more drops were put on top of the crankshaft before assembling the bearing caps then a bit more was added through the oiler holes. The crankshaft rotates very smoothly and has virtually no measurable radial play so I’m very happy with how these bearings have come out.

    Main Bearings 47.JPG Main Bearings 49.JPG Main Bearings 48.JPG

    Hopefully this will be of some use to anyone making a new, or repairing an old cast whitemetal bearing.
    The process is fairly easy and as long as some basic procedures are followed and some general care taken, you will end up with some of the smoothest rotating bearings you can get.
    Cheers,
    Greg.

  9. #9
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    Good stuff Greg and nice photos too.
    How many model engines have you built?

    John

    edit: Don't answer that, I just found your build thread on HMEM. Wow first engine build - very ambitious.

  10. #10
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    Hi John,
    Yep, this is my first model engine but I've restored a few full size stationary engines which often requires repairing parts or making new ones so this is not a huge leap.
    This engine is something I work on between other projects, it's taken a long time to get this far and I doubt I'll finish it anytime soon.
    Unlike restoration where the challenge is to make a part to the original spec, this is a blank canvas and I can do things how I want.
    There are no plans to follow so I have to work things out as I go and this is what I think I enjoy the most about this build.
    Cheers,
    Greg.

  11. #11
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    Default

    Absolutely fantastic stuff Greg!

    Beautifully written, photographed and most importantly, executed.

    Bob.

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